Hong Kong reported the first confirmed case of influenza A/H1N1 infection in the city on Friday, prompting authorities to immediately raise the flu alert level from "serious" to the highest level of "emergency".

"The patient is a Mexican arriving in Hong Kong on Thursday by air via Shanghai," Chief Executive Donald Tsang told reporters after an emergency meeting with senior officials of the Hong Kong Special Administrative Region (HKSAR) government.

Even before the emergency meeting concluded in the evening, the Department of Health ordered the MetroPark Hotel, where the patient has been living, to be quarantined.

Mexican patient arrived by air via Shanghai

The patient, a 25-year-old male, checked into the Metropark Hotel in Wanchai, Hong Kong, on Thursday afternoon and developed flu symptoms of lethargy, cough and a sore throat in the evening. He went to see the doctor at the nearby Ruttonjee Hospital at around 8:00 PM, Secretary for Food and Health York Chow said.

Preliminary tests thereafter showed the patient was positive for the new strain and further laboratory tests confirmed the result on Friday evening. The patient was currently in quarantine at the Princess Margaret Hospital and in stable condition.

Chow said the man arrived via Shanghai on Thursday afternoon but did not leave the airport in Shanghai, adding that the HKSAR government has informed the central government and authorities in Shanghai of the confirmed flu case.

But it was not immediately clear where the patient went to and how long he stayed at airport in Shanghai, Chow said.

The man sat at seat 23A aboard the China Eastern Airlines MU505and the passengers in the three rows before or behind the Mexican shall be quarantined, he added.

Hotel cordoned off, about 300 affected

The announcement on the case came after a daily briefing on the flu situation scheduled for the afternoon was abruptly canceled and senior officials of the HKSAR government were seen gathering for the emergency meeting.

The Metropark Hotel has also been cordoned off even before the emergency meeting concluded, and no one was allowed out of the hotel. Policemen and health security personnel outside the hotel were wearing masks, Xinhua reporters saw at the scene.

There are about 100 hotel staff members and 200 guests in the hotel, and they would be put in quarantine for 7 days from now, health officials said.

Medical personnel aboard ambulances arrived at the hotel in the evening later to take to hospital some of the guests that have developed flu-like symptoms.

A man was seen making a phone call at the lobby, telling someone on a cell phone that he was not allowed to leave the hotel and was wondering what had happened.